The present invention relates to electric switches and, more particularly, to an improved electric switch used in security alarm systems.
Almost all security alarm systems utilize a key operated control switch to permit an authorized person to enter a building, home, or the like without sounding the alarm. The control switch is turned ON to activate the system and OFF to deactivate the system. In security systems used to protect homes against entry by unauthorized persons, these control switches are often located adjacent frequently used entry and exit doors outside the home to encourage the homeowner to activate the system every time he leaves home. However, such externally located switches are susceptible to the tampering of a potential intruder. Thus, if a potential intruder wishes to deactivate the security system, he can do so by removing the control switch from its mounting and cutting, jumping or shorting out appropriate wires to disarm the system.
To prevent such tampering, most security alarm systems include a protective face plate covering the control switch to prevent unauthorized access thereto, and a hidden anti-tamper switch which activates the alarm system if the protective face plate is removed without first deactivating the system. The anti-tamper switch is generally of the normally closed or normally open type which is held in the open or closed position by the protective face plate, and which is biased to assume that position which activates the alarm when the face plate is removed. Thus, as above discussed, in order to tamper with the control switch, a potential intruder must first remove the protective face plate, however, removal of that face plate activates the system via the anti-tamper switch. A switch which can be adapted for use as an anti-tamper switch is shown in G. J. Meuer U.S. Pat. No. 2,065,904. As used herein, a "normally closed" switch is one which is closed when a face plate is on the unit. Likewise, a "normally open" switch is one which is open when a face plate is on the unit.
While effective, such a security system can still be circumvented if the anti-tamper switch is circumvented so that the face plate can be removed to provide access to the control switch for removal and deactivation thereof. Once the control switch is deactivated, the security alarm system is disarmed, and entrance can be easily effected by an intruder.
Heretofore, it has been assumed by security alarm system designers that switches such as the one described in the aforementioned Meuer patent are adequate protection against unauthorized removal of the protective face plate. Therefore, almost all known key-operated security alarm systems which are protected by a face plate, from the most inexpensive to the most complex, elaborate and expensive systems, use such anti-tamper switches. However, it is, in fact, an easy task to circumvent presently known anti-tamper switches. One simply ascertains what portion of the face plate is holding the switch in the depressed position, then drills a hole through the face plate at that ascertained position, and inserts a stiff rod, such as a coathanger, through the hole in the face plate to hold the anti-tamper switch in the depressed position. With the anti-tamper switch thus "artificially depressed", that is, depressed by the rod instead of the face plate, the protective face plate can be removed as the switch will not move into the circuit activating position upon removal of the face plate since the rod is held on the switch to keep it depressed. Once the face plate is removed, the control switch is exposed and can be moved into a position whereat the wires leading therefrom to the security alarm circuit are exposed, and the system can be deactivated by clipping, jumping, or shorting out those lead wires. Thus, even the most expensive and elaborate security alarm systems can be deactivated and thus defeated in a very short period of time by a semi-or unskilled intruder. Thus, no matter how elaborate and expensive, almost any known security alarm system employing a face plate is vulnerable to such easy circumvention by artificially maintaining the anti-tamper switch in the depressed position so that the switch does not sense the removal of the face plate which prevents access to the system control switch.
Even placing metal plates, or the like, in the protective face plate over the anti-tamper switch does not adequately prevent circumvention of that switch by the above-described method as high speed drills can be used to drill through even the hardest of plates.
It is noted that in order to circumvent the anti-tamper switch as above-described, the switch must be "artificially depressed", that is, held in the depressed position by means other than the protective face plate while that plate is being moved. The present invention provides an anti-tamper switch which is wired into the security alarm circuit to trigger the alarm immediately if an attempt is made to remove the face plate or artificially depress the anti-tamper switch while the security system is ON.